Worm Breeder's Gazette 8(3): 27
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
I've just begun to do some radiobiology using heavy ions from the Berkeley Bevalac accelerator as a way of modeling cosmic rays. NASA is interested in some biological dosimetry for heavy particles such as are encountered in earth orbit on the shuttle. Because of their true track structure, measurements in units such as rads and roentgens have dubious utility. Below are some preliminary results from iron irradiation experiments which looked for twitchers using Don Moerman and Dave Baillie's nicotine trick and some lethals using Raja Rosenbluth's eT1 balancer technique. The particles are highly mutagenic and I hope to eventually describe the types and extents of lesions caused by single particle interactions. An experiment using the BEVALAC accelerator at Lawrence Berkeley Laboratory was carried out on June 17, 1984. The purpose of this experiment was to familiarize us with the operation of the facility and to demonstrate the proof of concept that mutations could be induced in C. elegans using energetic heavy ions from the accelerator. Several tests were carried out but two are especially relevant here: 1) the induction of 'twitcher' mutants in gene unc-22 and, 2) the induction of lethal mutations in cross-over suppressed regions of chromosomes III and V using a reciprocal translocation strain. We were able to isolate 4 unc-22 mutants from 1965 N2 worms with gonads containing nominally 4, 10 and 30 cells with equivalent radiation doses of 30.02, 3.24 and 228.9 rads respectively. Several instances of male 'jackpots' were also noted. (A male 'jackpot' is the appearance of large groups of F1 males in broods of virgin hermaphrodites presumably due to induced X-chromosome loss; typical jackpots were 7 to 17 males per plate of 10 PO's whereas 0, 1 or 2 is normal). 6 lethal mutations and one long mutation were isolated from 96 adult worms tripley heterozygous for dpy-18 III, unc-46 V and the reciprocal translocation eT1(III;V) using an equivalent radiation dose of 3D.n2 rads. The type of radiation used was a beam of completely ionized iron particles having an energy of 445 MeV per nucleon or a total of 24.85 GeV per particle. The linear energy transfer of these particles was determined to be 198 KeV/micron and particles were delivered in pulses such that total fluence varied from about 10+E5 to 10+E7 particle tracks per cm2. Radiation characteristics were determined by Dr. E.V. Benton using CR-39 plastic radiation detector foils. We concluded that heavy ions are highly mutagenic in C. elegans and that the assays proposed in this proposal are capable of detecting genetic lesions induced by them. Work is in progress to determine the locations and nature of the new mutations. Confirming studies using alpha particles from Polonium - 210 also demonstrated the effectiveness of high LET particles. Mutations in unc-22 as well as several 'dumpy' and 'cell lineage defective' genes were induced with alpha particles using 1st stage larvae or dauer larvae as targets. The accompanying figure summarizes the BEVALAC results. [No accompanying figure]